Great topic you teed up. Some days my system sounds awesome and some days it doesn't quite get there. As noted above, "ear lube" helps my system and "swing lube" helps my golf game. I embrace lubricants for a variety of enhancements in my life. At any rate, the vicissitudes in the sound of one's system, day to day, is a matter that resides between one's two ears, I think.
Mood
Last night, listening before I went to bed, I was convinced there was something radically wrong with my system. Nothing sounded good. This morning I decided to play something I was sure would sound good. All of a sudden my mood picked up. Now everything I heard after that was reference sound quality.
I wonder if anyone else has had that kind of mood swing from one day to the next.